Deepwater Oil Exploration Fuels Composite Production
As the price of oil on the world market continues to climb, and as untapped land and shallow offshore oil reserves become a rarity, oil exploration companies are striking out into deepwater, developing reserves beneath the ocean floor a mile or more below the water’s surface. As a result, demand for strong yet lightweight materials able to stand up to the harsh subsea environment has spiked, with a corresponding peak of interest in composites. As the mid-year point in 2007 approaches, that interest has translated into action on many fronts, pushing several key projects beyond R&D, proposals and test installations into production for “live” projects.
Composite Rod-Reinforced Umbilicals Prepare for Service
A key deepsea well technology is the umbilical, a bundled collection of steel and/or thermoplastic tubing and electrical cabling used to transmit chemicals, hydraulic fluids, electric power and two-way communication and control between topside production vessels and subsea production equipment. Umbilicals typically range up to 10 inches (254 mm) in diameter, with internal tubes ranging from 0.5 inch to 1 inch (12.7 mm to 25.4 mm) in diameter. A dynamic umbilical is the portion of this key linking technology that is freely suspended from the semisubmersible platform to the sea floor, where it transitions to a static section that terminates at the remote subsea wellhead. Unlike the static component, a dynamic umbilical must withstand not only the stress of its own weight, but also must manage the uneven stress loads applied when it assumes its curved shape or catenary as it descends to its seabed connection.
Last year (see “Feature,” at left), Aker Kvaerner Subsea (AKS, Lysaker, Norway) introduced a dynamic umbilical that features an outer casing reinforced along its length with multiple carbon-fiber rods pultruded by Vello Nordic AS (Skodje, Norway). The rods feature longitudinal (0°) reinforcement with Panex 35 commercial-grade 48K carbon fiber tow provided by Zoltek Inc. (St. Louis, Mo.) wet out with vinyl ester resin supplied by Reichhold (Research Triangle Park, N.C.)
An initial order, placed by Kerr-McGee (Oklahoma City, Okla.) for its Merganser field off the southern U.S. coast in the Gulf of Mexico, has been augmented by several follow-on orders. Anadarko Petroleum Corp. (APC, Houston, Tex.) acquired Kerr-McGee in August of 2006 and then placed an order for three more carbon rod umbilicals plus 180 km/112 miles of AKS’s conventional steel umbilicals for static placement, making it the largest umbilical order ever placed.
“Carbon rod umbilicals were ideal for our application,” says Tim Dean, project manager for APC’s Merganser field. “You have a catenary in a mile and a half of water … and the deeper you go the more stress there is in the umbilical just to carry its own weight. For a very small premium, we knocked the stresses in the umbilical way down and greatly reduced our risk.”
APC began to install the static steel umbilicals during the summer of 2006. As CT went to press, only two static lengths awaited placement before the semisubmersible platform is moored to the seabed and four dynamic umbilicals can be installed to link the platform and well heads. APC was targeting completion of all umbilical installations in May and the beginning of production by third quarter 2007. However, strong currents in the Gulf have delayed installation, pushing the completion date into June.
Merganser is only one of 10 similar fields that eventually will tie back to the APC-operated Independence Hub, which will cover 1,800 square miles (4,662 km²) when the platform, fields and infrastructure are complete. Independence Hub will be the deepest offshore production facility in the world, a $2 billion semisubmersible platform operating in more than 8,000 ft (2,438m) of water. APC will operate eight of the ten fields. An additional order for AKS carbon rod-enhanced umbilicals has been placed by Hydro Gulf of Mexico LLC, a division of Norsk Hydro ASA (Oslo, Norway), to tie back its Q field to Independence Hub with a 12.2-mile/19.5 km umbilical. Also, Chevron (San Ramon, Calif.) has ordered a 9,500m/5.9-mile version for its Blind Faith field, elsewhere in the Gulf of Mexico. In the longer term, says Dean, “I would look for carbon rods in umbilicals that are suspended in water deeper than 5,000 ft or 6,000 ft. However, each design has to be evaluated based upon its unique requirements and environmental conditions.”
Composite Risers Rise to the Still Too-Rare Occasion
Composite risers have been the Holy Grail of composite applications in the oil and gas industry, not only because of their central role in the risky business of offshore oil production and their comparatively large diameters and correspondingly heavy use of composite materials, but also because they can offer real performance benefits vs. traditional steel, especially as offshore production moves to deeper water. Major players in the oil and gas industry have been at work on risers, including Shell, Conoco, AKS, ABB (now Vetco) and IFP (the latter developed composite choke and kill lines more than 20 years ago).
At AKS, for example, work is already well advanced on second-generation technology. Although the riser development enterprise Deepwater Composites, a joint venture between AKS and Conoco-Aker, was terminated on Dec. 31, 2005, the Deepwater Composites Group within AKS has strengthened and become an integral part of the company’s Riser Department. Group manager Kristian Per Grønlund notes, “Qualifications to certify metal work suppliers, welding companies and composite manufacturers were completed in 2006, resulting in a complete liner with metal-to-composite interface and AKS clip connectors.” The latter reportedly have an advantage over traditional flange-to-flange riser connectors in that the connection is both safe and simple, requiring less than one minute to complete. The coupling design load, according to American Petroleum Institute (API) Specification 16R, is 3.5 million lb/15,600 kN and tensile testing of a full-scale prototype showed no cracks at 6 million lb/26,700 kN. The clip connector was originally developed and tested by the French Petroleum Institute (IFP, Reuil-Malmaison, France) and is manufactured by AKS under license.
“Manufacturing of the AKS Next Generation Riser will commence during third quarter of 2007,” reports Grønlund. However, because this work results from a Joint Industry Project (JIP) completed in November 2006, AKS is searching for a project and operational partner to complete the next step, which would be an actual offshore field installation.
AKS isn’t alone. To date, few composite risers have been installed. For most riser developers, progress has slowed or stopped while they await a deepwater project that is connected to an operator who is willing to try composite risers. While operator hesitation is understandable — risers carry production fluids from the well, and failure could cost a drilling rig operator millions of dollars — industry sources say another deterrent is the long lead times in the manufacture of composite risers: Although well-tested designs are available and certified, there exists no dedicated production facility for composite risers anywhere in the world. That, however, is about to change.
New Riser Technology Scaled up for Production
Drawing on 30 years experience with umbilicals and other flexible tubulars, DeepFlex (Houston, Texas) is developing the first flexible, unbonded composite pipe for use as offshore risers and subsea flowlines and is constructing a dedicated, full-scale production facility on the Gulf of Mexico Coast. Historically, flexible tubing used in oil and gas production (a thermoplastic liner and steel outer casing) has been classified as bonded or unbonded. In the former, the liner and casing layers adhere to one another. Unbonded pipe, by contrast, consists of independent layers, which are not bonded, permitting them to “slip” in relation to one another, resulting in a more flexible construction. DeepFlex claims that its unique reusable, unbonded pipe, which has no metal layers, offers the lowest full life-cycle cost in the industry as well as better control of catenaries, lowest installation cost and increased water depth capacity due to its reduced weight and increased load capability.
Funded by a trio of oil and gas venture capital firms, including Chevron Technology Ventures LLC (Houston, Texas), Altira (Denver, Colo.) and Energy Ventures (Stavanger, Norway), DeepFlex expects its Gulf Coast plant will start up in mid-2008 and forecasts annual production of more than 300 km (190 miles) of linear pipe by the end of that year. DeepFlex also has patented a lightweight catenary system, comprised of proprietary external weights in the touchdown area, which put tension in their extremely lightweight, high-pressure tubulars that hang from floating production vessels and service subsea installations in water as deep as 3,000m (9,843 ft). This optimized installation prevents clashing with moorings and other risers, while eliminating the need for extra equipment required with heavier steel pipe, such as buoyancy modules and mid-depth arches.
Initially, DeepFlex pipe is being produced with inside diameters (ID) ranging from 2 inches to 8 inches (51 mm to 203 mm), but the upper limit will increase to 16 inches (405 mm) as production ramps up. These flexible, glass fiber-reinforced pipes are designed to handle maximum internal working pressures up to 5,000, 10,000 or 15,000 psi (345, 690 and 1034 bar), including a 2:1 safety factor, for use, respectively, in water depths of 1,000, 2,000 or 3,000m (3,280, 6,560 or 9,840 ft). This offers a range of products suitable for subsea risers and flowlines, water injectors and gas lift lines, etc., which are certified to meet or exceed the performance criteria of API standards 17J and 17B for traditional unbonded flexible subsea pipe. DeepFlex is currently working with an API and ISO committee to develop the first industry specification for a flexible fiber-reinforced pipe.
According to DeepFlex CEO Bruce McConkey, “Our competition is not the Fiberspars of the world, who make bonded, filament-wound composite pipe, but instead the manufacturers of metal flexible pipe, like Technip, Wellstream and NKP Flexibles, as well as other metal technologies, such as steel catenary risers [SCRs] and pipe-in-pipe.” While bonded pipe does not offer the truly flexible characteristics that unbonded pipe does, DeepFlex also contends that pipes made by filament winding are limited in length to the bobbin size, unless fiber ends are spliced. McConkey differentiates the DeepFlex process: “We engineered a unidirectional composite tape and found a vendor to make it to our exact specifications.” The proprietary reinforcing machines hold up to 3 million ft (914,400m or 568 miles) of tape. “They produce the specifically designed pipe we want in truly continuous lengths,” he maintains.
The precured uni tapes are 60 percent fiber by volume, and although carbon, S-glass and Kevlar 29 and 49 fibers have been tried, DeepFlex says E-glass reinforcement yields the best combination of properties when used with the company’s proprietary epoxy-based resin. Beginning with one of several industry-standard, chemically resistant, continuously extruded thermoplastic liners, the process involves overwrapping the liner with three basic types of composite reinforcement: pressure, hoop and tensile reinforcement drawn from as many as 240 spools. The number and thickness of the wafer-thin (30 mil to 50 mil/0.0762 mm to 0.127 mm) tapes remains constant, but smaller ID pipes use narrower tapes. The tapes are bonded vertically into stacks to create a “thick” composite. However, these stacks are not bonded side-by-side. Further, the pressure, hoop and tensile stacks are not bonded to each other.
The innermost reinforcement is the pressure wrap, typically two layers of contra-helically wound precured tapes, with the opposing angles providing support for both circumferential and longitudinal forces generated by internal pressure in the liner. The following hoop reinforcement normally comprises multiple composite tapes wound at an angle specifically calculated to withstand external compressive loads. The final tensile wrap, like the pressure wrap, comprises two contra-helically wound precured tape layers, placed at angles that bear tensile loads other than those generated by internal pressure (for example, longitudinal loads imposed as the tube is suspended from platform to sea bottom). Each reinforcement layer is separated from the next by an extruded thermoplastic polymer membrane, which is not required for performance but simply provides an antifriction surface. McConkey explains that each reinforcement layer performs to the maximum pipe specifications on its own, without help from the other two layers, enabling DeepFlex to further customize its products to offer “designer pipe.” “We have a containment layer, an anticollapse layer and a tensile layer, all of which can be altered, strengthened or lightened to meet specific customer needs.”
A final extruded thermoplastic jacket protects the functional wrappings from incidental damage when the pipe is spooled, reeled, transported and installed in the same manner as metal flexible pipes. As with the initial thermoplastic liner, any elastomer that can be extruded can be used for this outer jacket, with the most common being Nylon 11, high-density polyethylene (HDPE) and polyvinylidene difluoride (PVDF).
DeepFlex is producing commercial pipe in its Wisconsin pilot plant for its first order, a short-length “jumper” application in 7,000 ft (2,134m) of water.
Composite Fire Suppression System Installations Multiply
In 1988, the Piper Alpha, an offshore platform in the North Sea, caught fire, killing 167 men. Before Piper Alpha, fire safety regulations mainly stressed water deluge systems. Minimal passive fire protection was mandated, and what was suggested was typically only for the faces of bulkheads, control rooms and crew accommodations. After this disaster, new safety standards specified not only rapid detection and reliable shutdown of fuel feed to a fire but also passive fire suppression systems that limit the temperature on the unexposed sides of all key structures, enabling containment of the fire on the exposed side. These systems must withstand, in testing, the effects of simulated hydrocarbon fires and the huge thermal loads and mechanical forces following ignition of pressurized hydrocarbons, known as jet fires.
Solent Composite Systems Ltd. (SCS, Isle of Wight, U.K.) developed its ProTek passive fire protection and blast restraint systems to meet the new regulations. ProTek composite enclosures, for exam-ple, can withstand two hours of jet fire temperatures as well as explosion blast and direct flame while maintaining an interior temperature of 65°C/149°F or below, so that protected equipment remains operative. ProTek enclosures are used for Emergency Shut Down Valves (ESDV) and actuators, firewalls, blast walls, bulkheads and marine fire partitions, escapeways, under-deck fire protection, riser hang-off and splash-zone protection, and passive fire protection (PFP) for flexible risers and pipes. On offshore platforms, redundant ESDVs are mounted in pipelines and marine risers to stop the flow of oil or gas to the platform and ensure that fires aren’t fed from the well. ProTek composites also are used as protective encapsulations for subsea equipment.
ProTek enclosures are made from composite sandwich panels comprised of six different layers. The front and back fiber-reinforced epoxy structural skins, at minimal weight, can withstand high blast pressure. Two insulation cores, one phenolic foam and the other ceramic, reduce heat transfer across the panel plane and through the panel thickness, while an external epoxy-based ablative layer provides jet fire resistance and is surfaced with a protective white gel coat that provides long-term weather resistance. The composite layers are made using both woven fiberglass and carbon fabrics. Laminates are hand layed and then either compression molded or oven-cured, depending on the configuration of the structure. Vacuum infusion processing may be used as an interim step. All structures are cured at elevated temperatures. Typical panel weight is 25 kg/m² (5 lb/ft²) for a 50-mm/2-inch wall thickness, and panel thickness ranges from 10 mm to 70 mm/0.4 inches to 2.8 inches. Enclosures vary in height from 4m to 9m (12 ft to 25 ft) with a footprint of 3m² to 6m² (32 ft² to 64 ft²), designed to protect valves ranging in size from 2 inches to 42 inches (51 mm to 1,067 mm) in diameter.
SCS refers to ProTek’s enclosures as “fit and forget” solutions, because the structures combine a high degree of design flexibility with corrosion-free materials and a zero maintenance lifespan of 30+ years. What might, for cost reasons, be limited to simple rectangular boxes in conventional and more expensive stainless steel, can, with composites, easily be designed to fit closely around unusually shaped equipment (see photo, this page). Further, SCS can mold in through-holes and vents for cables and pipes and accommodate almost any constraints imposed by the site layout. Rapid access to equipment also is provided via lift-off hatches.
Although ProTek enclosures are initially more expensive than the “quick-fix” soft jackets commonly used when fire and blast protection are considered late in a project, soft jackets typically require replacement five to six times during the project lifecycle. In fact, soft jacket performance in offshore environments is now considered so poor that the latest Norwegian standard precludes its use.
SCS has placed more than 600 ProTek structures in Europe since 1991. Recently, Statoil and contractor Aker Stord selected ProTek for ESVD protection at its Snøhit processing plant on Melkøya Island near Hammerfest, Norway. ProTek already had a good track record with Statoil, having been used for ESDV, actuator, riser hang-off and end-connection protection on its Norne FPSO vessel, following similar successful installations on the Åsgard A, Åsgard B and Sleipner offshore platforms. The Norne installation was unusual in that it integrated the riser, actuator and ESDV protection into a single ProTek assembly. For the Hammerfest plant — Europe’s first export facility for liquefied natural gas (LNG), 60 percent of which will be sent to the U.S. — SCS installed 116 composite fire and blast enclosures, which also must withstand the extreme arctic environment of this facility on the Barents Sea.